You people are underestimating Gaara hard. Think about it he's 13 years younger than Mei the second youngest Kage of the group Which puts him easily 20 years younger than the rest of the group and he's still able to hold his own with them. If Gaara had those 13 years to grow and train he would better than the other Kages, who have reached their peaks already. Seriously none of them are advancing their techniques at this point, they've powered up they're go to jutsu and they're sticking with those while Gaara's been growing and coming up with new jutsu to use since part 1.